Chapter 3: Cell Structure - Bacterial Cell Wall

Question 1

What is the bacterial cell wall?

Answer 1

• Semi-rigid structure giving shape to the cell

Question 2

What are the functions of the bacterial cell wall? (3)

Answer 2

• Major function is to prevent rupture of the cell
• protect against environmental changes
• Useful in the identification of bacteria ie. gram stain

Question 3

What complex macromolecule is the bacterial cell wall made of?

Answer 3

peptodiglycan

Question 4

What is peptidoglycan? (3)

Answer 4

• Mesh-like structure composed of polysacharrides and amino acids
• Polysaccharide portion is composed of two alternating polysaccharides
• Protein portion is composed of short AA chains

Question 5

The polysaccharide portion of peptidoglycan is composed of what two polysaccharides?

Answer 5

N-acetyl glucosamine (NAG)
N-acetyl muramic acid (NAM)

Question 6

What is the structure of peptidoglycan? (3)

Answer 6

• polysaccharide chains run parallel
• Peptide chains link polysaccharides together
• Forms a mesh-like net surrounding the cell

Question 7

What is the Gram positive cell wall structure? (3)

Answer 7

• Made of thick layers of peptidoglycan outside the plasma membrane
• contains teichoic acids (wall techoic and Lipotechoic)
• has only one membrane, the cytoplasmic membrane

Question 8

Where does the wall techoic acid attach to?

Answer 8

peptidoglycan

Question 9

Where does the lipotechoic acid attach to?

Answer 9

• plasma membrane and extend through the peptodiglycan

Question 10

What is the structure of the Gram negative cell wall?

Answer 10

• Thin peptidoglycan layer that is sandwiched between two membranes
• outer membrane made of lipids (phospho), proteins, and lipopolysaccharides (LPS)

Question 11

What is the polysaccharide portion of lipopolysaccharides composed of? (2)

Answer 11

• Q-sugars
• useful for distinguishing Gram negative bacteria

Question 12

What is the lipid portion of lipopolysaccharides? (2)

Answer 12

• toxic
• referred to as endotoxin (prevalent in gram -)

Question 13

In lecture, what are exotoxins? (3)

Answer 13

• toxins produced by bacteria but travel outside to affect the host
• acquired from external source
• in both gram - and +

Question 14

How does the Gram positive stain work? (2)

Answer 14

• Thick peptidoglycan traps the crystal violet
• stains purple
  see slide 29

Question 15

How does the Gram negative stain work? (3)

Answer 15

• Thin peptidoglycan does not trap crystal violet, and the outer membrane gets disrupted by alcohol
• crystal violet is wash away
• Safranin counterstain stains the cells pink
  see slide 30

Question 16

Why is peptidoglycan special? (5)

Answer 16

• diff. from anything found in animal cells
• many antibiotics have been discovered that act against peptidoglycan
• ex. penicilin, which inhibits production of peptidoglycan
• Degraded by one of our own natural defenses, lysozyme
  —-> found in tears, saliva, mucous

Question 17

What is the cytoplasmic membrane (plasma or cell membrane) composed of? (2)

Answer 17

• phospholipid bilayer
• exists in a semi-fluid state

Question 18

What is the function of the cytoplasmic membrane? (3)

Answer 18

• separats in interior (cytoplasm) from the outside environment
• serves as a semi-permeable barrier
• selectively allows the inflow and outflow of materials

Question 19

What antimicrobial agent disrupts the cytoplasmic membrane? (2)

Answer 19

• alcohols
• can be used as a disinfectant

Question 20

In lecture, why is 70% alcohol better than 100% (4)

Answer 20

• 100% evaporates faster
• alcohol coagulates the proteins in bacteria cell wall to allow the microorganism to die
• 100% disrupts the cell membrane without coagulation
• 100% is more expensive